1. Field of the Invention
This invention relates to metal oxide-hydrogen batteries.
2. Prior Art
Within the prior art, a variety of techniques and materials are utilized for assembling metal oxide-hydrogen cells to form operative batteries. The commonly used method of connecting electrodes in series is termed to be the bipolar connection method, and the basic feature of that system is that the positive electrode of a single cell and the negative electrode of the adjacent single cell are combined in one structure. This structure has as its function the electrical connection of the two electrodes and the separation of the electrolytes in adjacent cells. It is often utilized to separate the positive and negative electrode reactants in situations where they are not contained in the electrodes themselves. This prior art metal oxide-hydrogen battery of bipolar construction is shown schematically in FIG. 1. The stack 10 in FIG. 1 generally comprises a negative electrode 12, a positive electrode 14 and metal screen 16 separating the two electrodes. Individual electrodes are separated by means of a separator element 18. It should be noted that in this prior art construction, the positive and negative electrodes of adjacent cells are connected electrically by the metal screen 16, and the screen must also separate the electrolytes from different cells. In the prior art, a screen must be utilized instead of a solid plate so that gas has access to the hydrogen electrode (negative). This conventional design has several disadvantages.
First, the possibility of electrolyte contact between two cells still exists. In situations where long cell lifetimes are required, the danger that some electrolyte will be trapped in the screen thereby electrochemically shorting the cells becomes a major design consideration. Within the prior art, the use of a thick screen has been proposed to reduce the likelihood of such an occurrence, but at the expense of weight and volume in the cell increasing. Also, it is readily apparent that the use of heavier or thick screens increases the electrical resistance of that element. Another disadvantage with the prior art technique is that the metal electrode (positive) is discharged unevenly, that is, only from one side. This uneven discharge rate can lead to differential stresses between sides of the electrode which may result in buckling. In areas of high pressure where current density becomes extremely high, this buckling can lead to electrical shorting or cause high temperatures which would destroy the separator 18.
Additionally, prior art cells, as typified by FIG. 1, exhibit relatively high weights because one metal screen is used per metal oxide electrode, and, additionally, the screens themselves are relatively heavy. This high weight of the screen results from the thickness required to function as a separator and, additionally, from the small spacing of the mesh wires necessary to provide adequate support of the electrodes. Finally, because an adequate rate of heat rejection is necessary, the diameter of the prior art metal oxide-hydrogen cell stack cannot be made arbitrarily large. The total battery voltage, usually a fixed design factor, determines the number of plates used which combine with the maximum plate diameter, then determines the maximum energy content of the cell. Accordingly, making cells with large energy content is difficult utilizing bipolar construction techniques.
Also, within the prior art a variety of variations of the basic system denoted in FIG. 1 is known. For example, the patent to Tsenter et al., U.S. Pat. No. 3,669,744, shows in general configuration a hemispherically sealed nickel-hydrogen storage cell wherein a hemispherically sealed storage cell consisting of a nickel oxide electrode 1 and a negative hydrogen electrode 2 is disposed in a tank 3, each of the electrodes separated by a separator in vertical alignment. This patent emphasizes the problems of generating sufficient power vis-a-vis gas pressure requirements by an optimization of thickness ratios of the positive and negative electrode. Also, U.S. Pat. No. 3,716,413, Eisner, discloses a cell arrangement utilizing a center shaft 17 disposed on a cell case 10 to which electroes 11 and 13 are concentrically mounted. A series of bus bars 12 and 14 are also shown in Eisner in a parallel arrangment with the center shaft. The center shaft 17 broadly serves as a means of orientation of the electrodes within the cell.
As an alternative to the Eisner system, various other patents, such as U.S. Pat. Nos.: Niedrach, 3,297,484; Geltling, 3,436,272; Rohr, 3,505,114; Titterington, 3,607,215; and Louis et al., 3,833,424, all disclose fuel cell arrangements wherein electrode stacks are joined by a sequence of threaded bolts disposed along the periphery of a cell stack. Typical of this group is the patent to Louis et al in which a series of bolts 20 are disposed in clamping boards 26 to 29. Similarly, Niedrach discloses a series of bolts 19 utilizing spacers 20 with end plates 10 and 14 as the means of clamping the electrode structure together.
Additionally, the prior art is replete with numerous patents dealing with other techniques of construction of cell subcomponents. For example, patents to Giner, U.S. Pat. No. 3,739,573, and Dennison, U.S. Pat. No. 3,834,944, disclose cylindrical fuel cells which may be stacked and electrically connected in series. The Giner patent is of interest in that it discloses the use of a palladium foil with a palladium black surface saturated with hydrogen as one electrode composition and a separator of an electrolyte matrix in the form of asbestos soaked with a selected electrolyte. Additionally, patents to Gray, U.S. Pat. No. 3,617,385, and Winsel, U.S. Pat. No. 3,660,166, disclose vertical fuel cell arrays which are connected in series.
More recently, the technique of back-to-back electrode stacking has been evaluated. The inventors first discussed this generalized technique in the "Proceedings of the 9th International Symposium," Brighton, England, 1974, published in POWER SOURCES 5, 1975 (Academic Press). Although conceptualized, no definitive cell or battery structures were contemplated by that scientific teaching. The inventors have built upon those concepts to achieve complete, operative structures.